How do i find the units in a math problem?

1 Answer
May 20, 2018

I have an example in the Explanation section.

Explanation:

Many math problems do not need units -- such as
#2x=5, x=?#
I don't know the situation giving you a problem, but I will guess.

My advice is, while working the problem, keep the units with all the given data and let the units flow or cancel according to the rules of algebra. Consider a simple speed question:

At a speed of #50 (km)/h# , how long will it take to go #220 " km"#?

The basic formula for speed (or velocity) is v = d/t.

To solve this problem, we want the time, t, by itself on the left side of the equation. So multiply both sides by #t/v# and cancel where possible.

#(t/cancel(v))*cancel(v) = (cancel(t)/v)*d/cancel(t)#

#color(red)("Therefore " t = d/v)#

Now plug in the given data, with units

#t = (220 cancel(km))/(50 cancel(km)/h = 4.4 h#

You do not need to figure out that the units of the answer is h (for hours), it automatically is there if you do the algebra properly.

There is another advantage: suppose you messed up when solving for time (the line above that I put in #color(red)(red)#) so that you got #t = d*v#. In that case, you would get units of #m^2/h#. That would look very wrong and cause you to look for a mistake in your work.

I hope this helps,
Steve